The invention relates generally to optoelectronic/optical transceivers and particularly to optoelectronic/optical transceiver modules that benefit from an efficient use of module space.
Today, communication systems using optical fiber as a means for transmission are widely employed for a variety of purposes ranging from a basic transmission line in public communication channel to a short-distance network such as a LAN (local area network). Since most of the devices connected by these optical fibers are electronic devices rather than optical devices, optical transceivers are commonly placed at the interface between the optical fibers and the electronic devices. An optical transceiver includes an optical transmitter that receives electric signals and converts them into optical signals, and an optical receiver that receives optical signals and converts them into electric signals.
Optical transceivers are commonly packaged in the form of a transceiver module that can be mounted on a motherboard of one of the electronic devices. These electronic devices to which an optical transceiver may be attached are commonly referred to as “host devices.” As optical transceivers become more prolific, standards are imposed so that manufacturers of host devices do not have to custom-order transceivers. Unfortunately, these standards ultimately become constraints that conflict with the transceiver designs that call for bigger optical transceiver modules. For example, while a size standard imposes a maximum allowable size of a transceiver module, certain components in the optical transceiver module must be placed far apart in order to reduce crosstalk and electromagnetic interference. More specifically, the transmitter and the receiver should be spaced far apart and shielded from each other because the optical transmitter, which requires a relatively high current for modulation of a light emitting element (e.g., a laser diode), can interfere with the optical receiver which operates with a relatively low current obtained from the light receiving element. Also, to ensure that electrostatic discharge effects will not be significant, it is desirable to place the components away from the housing of the optical transceiver module. However, doing so increases the size of the printed circuit board inside the module since the edges of the printed circuit boards cannot be utilized and conflicts with the size restriction imposed by the standard.
One attempt to meet the size restriction while separating certain components by a minimum distance involves coupling the transmitter and the receiver to two different sides of a single printed circuit board. FIGS. 1–5 show an exemplary embodiment of a conventional single-board transceiver 30 including a transmitter module 32 (e.g., TOSA) and a receiver module 34 (e.g., ROSA) mounted on one printed circuit board (pcb) 36 that is configured to fit inside a standard transceiver module housing. If pcb 36 is a double-sided printed circuit board, the receiver module 34 and the receiver circuitry may be mounted on one surface of printed circuit board 36, while the transmitter module 32 and the transmitter circuitry may be mounted on the other surface of the printed circuit board. Connector pins 39 are soldered on to pcb 36, as shown in FIG. 2. The connector pins 39 should be arranged to meet the configuration imposed by the relevant optical communication standard. Then, as shown by an arrow in FIG. 3, the transceiver 30 with connector pins 39 is placed in a lower housing 40, which is designed to meet the standard size restrictions. The lower housing 40 comprises a base 42, sidewalls 44, and a network interface enclosure 46. The network interface enclosure 46 is divided into a first section 48 for housing the transmitter 32 and a second section 49 for housing the receiver 34. The division of the network interface enclosure 46 into two sections helps reduce crosstalk between the transmitter 32 and the receiver 34 because the lower housing 40 is made of a shielding material. FIG. 4 shows a transceiver module 50, which is a combination of the transceiver 30 and the lower housing 40. When an upper housing 52 is disposed to cover the lower housing 40, the result is the completely enclosed transceiver module 50, as depicted in FIG. 5. The upper housing 52 is designed to snugly fit around the sidewalls 44 of lower housing 40, and have slots through which pins 39 can protrude and be coupled to a host device.
However, the single-board optical transceiver module 50 has disadvantages. Where the transmitter 32 and the receiver 34 are coupled to different surfaces of the pcb 36, for example, two controllers (one on each surface) may be necessary to control both components, raising the cost of the transceiver and wasting valuable board surface. Further, since the transmitting circuit is greater in circuit scale than the receiving circuit, the size of the printed circuit board is, to an extent, determined depending on the circuit scale of the transmitting circuit. Consequently, a sufficient margin space is left on the surface of the printed circuit board where the receiving circuit is to be disposed, again leading to a waste of valuable board space. As host devices operate at higher performance levels with faster data transfer rates, it becomes desirable to squeeze more circuitry into an optical transceiver module. In light of this increased need to efficiently use the volume of the transceiver module, such waste of the board space becomes highly undesirable. A transceiver configuration that allows a more efficient use of space for higher circuit density is desirable.